. >> reporter: two letters, one to president obama, another two roger wicker, showed initial positive results in field tests. the letters never reached the white house or capital. >> the mail sent here is screened and the tests are taken at remote sites to mitigate the risks. >> the first was stopped then miles from its target to capitol hill. the second letter to the white house was intercepted six and a half miles away on a military base on the outskirts of d.c. a third post office sorting facility suffered possible contamination to its filtering system from an unknown source, ten miles from downtown washington. protections including air sensors at screening centers, set up after the anthrax attack in 2001, that killed five americans and injured 17 others, it happened just after 9/11. today's apparent attempt, so close to another incident of domestic terror is an eerie reminder of those frightening days. >> the letters to the problem and the senator were both signed with the initials k.c. which matches the name of the man arrested in tupelo, mississippi. diane? >>> and now we turn t